1. Technological Field
The present disclosure relates generally to the field of data networking and telecommunications. More particularly, in one exemplary aspect, the present disclosure is directed to scrambling symbols over multi-lane serial interfaces in order to improve undesired electromagnetic emissions.
2. Description of Related Technology
Many serial communications systems send data over more than one lane or channel. Commercial examples include without limitation, DisplayPort, HDMI (High-Definition Multimedia Interface), etc.
As is well known within the electrical arts, rapid signaling changes in a transmission line will generate undesirable electromagnetic interference (EMI) in neighboring circuitry and/or devices. Consequently, in order to reduce EMI, certain technologies (such as for example and without limitation, DisplayPort, Firewire, etc.) utilize a transmitter “scrambler” that is configured to add/spread the signal with pseudorandom noise; the resulting “scrambled” signal has a reduction in peak spectral noise, and a wider spectral “footprint”. The receiver has a corresponding “descrambler” which can remove the pseudorandom noise and reconstruct the original signal. Many types of pseudorandom number generators exist; however, scramblers are typically implemented with linear feedback shift registers (LFSRs) due to the simplicity and relatively inexpensive cost.
One problem with multi-channel scrambling technologies (such as DisplayPort, etc.) occurs when the same data is transmitted on each channel. For example, during video data transmissions so-called “blanking” intervals can include long periods of null data which are typically represented with the same value (e.g., all zeros (0) or all ones (1)). Under these circumstances, the scrambled result for each lane of the multi-lane transceiver is identical (each lane transmits the same value, which is identically scrambled). Since each lane is perfectly correlated with the other lanes, the overall EMI magnitude of the multi-lane transmission is a direct sum of each of the contributing EMIs. The resulting spectral footprint of the multi-lane transmission line may be strong enough to interrupt nearby circuitry. Large EMI can be especially problematic for devices that have very aggressive form factors (i.e., where components are in very close proximity).
Accordingly, improved apparatus and methods are needed in order to address these EMI concerns with regards to multi-lane serial bus technologies such as e.g., DisplayPort, etc. More generally, such apparatus and methods would ideally provide for mechanisms that improve the EMI characteristics of multi-lane high speed serial bus operation, while also advantageously leveraging existing hardware in certain implementations so as to minimize circuitry costs in future implementations.